1. Technical Field
The present disclosure relates to a display device and a driving method thereof, and more particularly, to a display device including a panel with a built-in touch panel and a driving method thereof.
2. Discussion of the Related Art
Touch panels are a type of input device included in or built into display devices such as liquid crystal display (LCD) devices, plasma display panels (PDPs), organic light emitting display device (OLED), and electrophoretic displays (EPDs). A touch panel enables a user to input information by directly touching a screen of a display device with a finger, a pen or the like while looking at the screen of the display device.
Particularly, the demand for display devices integrated with in-cell type touch screens is recently increasing. In-cell type touch screens include a plurality of built-in elements configuring the touch screen for slim portable terminals such as smart phones and tablet personal computers (PCs).
In-cell type display devices may be categorized into mutual display devices and self-capacitive display devices.
FIG. 1 is an exemplary diagram illustrating a configuration of a related art mutual display device. FIG. 2 is an exemplary diagram illustrating a related art self-capacitive display device. FIG. 3 is an exemplary view illustrating a cross-section taken along line C-C′ of FIGS. 1 and 2.
A mutual display device 10, as illustrated in FIG. 1, includes: reception electrodes RX1, RXn-1, RXn (collectively referred to herein as a reception electrode RX) formed in a block form in parallel with a data line in a display area A of a panel; driving electrodes TX1, TXm-1, TXm (collectively referred to herein as a driving electrode TX) configured with a plurality of driving electrode parts 11 which are disposed with the reception electrode RX therebetween, and is formed in parallel with a gate line in the display area A; a display driver 19 that is provided in a non-display area B of the panel that controls the data line and the gate line, and applies a common voltage or a touch driving voltage to the driving electrode TX and the reception electrode RX; a reception electrode line 15 that extends from the reception electrode RX, and is connected to the display driver 19; a driving electrode line 12 that extends from the driving electrode TX in parallel with the data line, and is connected to the display driver 19; and a touch driver (not shown) that determines whether there is a touch, by using the driving electrode and the reception electrode which are connected to the touch driver through the display driver.
A self-capacitive display device 20, as illustrated in FIG. 2, includes: a plurality of touch electrodes 21 that are formed in a display area A of a panel; a display driver 29 that is provided in a non-display area B of the panel, and drives the touch electrodes 21; and a touch driver (not shown) that is connected to the touch electrodes 21 through the display driver 29, and determines whether there is a touch. In this case, in each of the touch electrodes 21, a touch electrode line 22 is formed in parallel with the data line. Also, when the number of width-direction touch electrodes is Q number and the number of height-direction touch electrodes is P number, the touch driver (not shown) includes a total of n (where n is Q×P) number of sensing units.
In the display device, a cross-sectional surface taken along line C-C′ of FIGS. 1 and 2 is as illustrated in FIG. 3. Referring to FIG. 3, in the in-cell type display device, a gate insulating layer 10b (20b) is coated on a base substrate 10a (20a), and a data line 10c (20c) is formed thereon. A buffer layer 10d (20d) is coated on the data line 10c (20c), and an insulating layer 10e (20e) is formed thereon. The driving electrode line 12 (or the touch electrode line 22) and a pixel electrode 10f (20f) are formed on the insulating layer 10e (20e), a protective layer 10g (20g) is coated thereon, and the driving electrode part 11 (or the touch electrode 21) is formed thereon. In FIG. 3, units Nos. 10 to 19 denote elements of the mutual display device illustrated in FIG. 1, and units Nos. 20 to 29 denote elements of the self-capacitive display device illustrated in FIG. 2. In FIG. 3, as an example of the driving electrode parts 11, a #(m,1)th driving electrode part 11b of FIG. 1 is illustrated, and as an example of the touch electrodes 21, a #Pth touch electrode 21b of FIG. 3 is illustrated.
Here, referring to FIGS. 1 to 3, the driving electrode line 12 connected to a #(1,1)th driving electrode part 11a is disposed with the protective layer 10g between the driving electrode line 12 and the #(m,1)th driving electrode part 11b. 
Also, referring to FIGS. 1 to 3, the touch electrode line 22 connected to a #1st touch electrode 21a is disposed with the protective layer 20g between the touch electrode line 22 and a #Pth touch electrode 21b. 
During a touch sensing period, in the mutual display device of FIG. 1, different touch driving voltages are supplied to the #(1,1)th driving electrode part 11a and the #(m,1)th driving electrode part 11b, and thus, as illustrated in FIG. 3, a parasitic capacitance D is generated between the driving electrode line 12 connected to the #(1,1)th driving electrode part 11a and the #(m,1)th driving electrode part 11b. 
Moreover, during the touch sensing period, in the self-capacitive display device of FIG. 2, the same touch driving voltage is supplied to the #1st touch electrode 21a and the #Pth touch electrode 21b, but since the touch electrode line 22 connected to the #1st touch electrode 21a is adjacent to the #Pth touch electrode 21b, as illustrated in FIG. 3, the parasitic capacitance D is generated.
The parasitic capacitance D can cause noise. Due to the noise, a touch sensitivity can be reduced, or a touch error can occur.
In the related art mutual display device and the self-capacitive display device, during the touch sensing period, the driving electrode part 11 and the driving electrode line 12 or the touch electrode 21 and the touch electrode line 22 are parallelly disposed with the protective 10g or 20g therebetween, and for this reason, the parasitic capacitance D that is a cause of noise is generated between the two elements.
FIG. 4 is a waveform diagram showing an image output (‘display’) period and a touch sensing (‘Touch’) period in the related art in-cell type display device, and FIG. 5 is an exemplary diagram showing a waveform of a touch driving voltage supplied to a driving electrode and a reception electrode in the related art mutual display device.
In the related art mutual display device and self-capacitive display device, as shown in FIG. 4, the image output period and the touch sensing period are temporally divided (e.g., mutually distinct, non-overlapping, and optionally, interleaved).
Particularly, a touch panel applied to the mutual display device of FIG. 1 includes a driving electrode TX, which receives the common voltage (Vcom) in the image output (‘display’) period and receives the touch driving voltage in touch sensing period, and a reception electrode RX which receives the common voltage in the image output period, and receives a reference voltage in the touch sensing period.
In this case, in the touch sensing period of the mutual display device, block dim can occur in a panel of the mutual display device due to a difference between root mean square values (Vrms) of voltages respectively input to the driving electrode TX and the reception electrode RX.
That is, during the image output period, the common voltage Vcom is supplied to the driving electrode TX and the reception electrode RX.
However, during the touch sensing period, as shown in FIG. 5 (a), a pulse-type touch driving voltage is supplied to the driving electrode TX, and as shown in FIG. 5 (b), the reference voltage VRX_REF is supplied to the reception electrode RX. The touch driving voltage swings between the maximum value VTX_HIGH and the minimum value VTX_LOW. The value of VTX_LOW is also equal to the value of VRX_REF.
In this case, as shown in FIG. 5, a root mean square value TX_RMS of the touch driving voltage is a value between the common voltage Vcom and the maximum value VTX_HIGH. The reference voltage VRX_REF is the same as a root mean square value RX_RMS of the reference voltage. The root mean square value TX_RMS of the touch driving voltage differs from the root mean square value RX_RMS of the reference voltage.
Therefore, in the panel of the mutual display device, block dim can occur due to a difference between the root mean square values.